DE3025504A1 - CABLE WITH GREAT IMMUNITY AGAINST ELECTRO-MAGNETIC IMPULSES (EMP) - Google Patents

Description

The symmetrical electrical cables (such as the twisted Cable pairs) represent the balanced lines and are therefore the parasitic electrical and magnetic Not very sensitive to external fields. The asymmetrical electrical cables (such as a coaxial cable) represent unsteady lines, but in which the structure of the outer conductor forms an armor that is normal any influence of parasitic electrical and magnetic external fields (exact case of armor in the full pipe), as well as foreign surface currents generated by these fields.

However, the imperfections inherent in the practical manufacture of these cables, such as the fact that the Armouring of a coaxial cable (because of the flexibility) consists of a braid, cause in practice this Structures of these fields are sufficiently penetrated to render their immunity inadequate in the case of weak Amplitude transmitted signals and / or of particularly intense interference fields.

To produce cables with high immunity, one superimposes in these cases:

- pairs of cables or other balanced structures; an electrical screen, possibly followed (outwards) by a magnetic screen, etc .;

- a coaxial cable: a magnetic screen (over the armor braiding), possibly followed (to the outside) by an electrical screen, etc.

Such immunized structures are well known and described in the literature, such as, for example, "Use of magnetic materials for improvement of screening properties of different types of cables; LAURI HOLME and JOAKKO ANNANPOLO? IEEE Electromagnetic Comptability Symposium 1973 Record, pages 340-357 ".

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It is therefore a conventional process to create magnetic-metallic layers in the form of braiding or in the form of ribbons to use which with iron, steel, iron-nickel alloys with high magnetic permeability, amorphous magnetic Alloy etc. are wound, which at the same time increase their conductivity and their magnetic permeability contribute to immunity "

Fig. 1, for example, gives the general diagram of such a protected cable considering a conventional coaxial cable, which is provided with a magnetic and an additional conductive shield, again.

In this figure, 1 means the classic center conductor

of the coaxial cable, 2 the classic insulating dielectric

(full, ventilated, sliced, etc.), and 3 the armor plating

tion, whereby the transmission cable is represented.

4 means a flexible layer, i.e. "a tape, a jacket or a braid of conductive metal or conductive magnetic alloy (kind of soft iron, steel or for high performance Mu-metal, Permalloy, Metflas, wound with covering turns), and 5 a highly conductive, magnetic or non-magnetic armoring (braiding, wrapping, tape, etc.) (usually copper is used in the case of a braid and steel tape in the case of a cable with high mechanical strength).

Finally, 6 represents an external mechanical protective layer (plastic, elastomer, etc.).

In such an embodiment, the magnetic layer 4 at the same time plays the role of increasing the impedance of the, by the exterior of the braid 3 and the interior of the armor 5 self-induction coefficient formed "as well as the role of a magnetic armor represented by the coaxial structure.

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Of course, however, the use of such leads Layer or layers of this kind in the case of the superimposed structures lead to a great reduction in flexibility of the cable on the one hand and susceptibility to bending, vibrations, etc. on the other.

Of course, such layers 4 are not only sensitive to wrapping or the formation of braids in the manufacture of the cable, but they are also subject to highly variable performances during the service life of the cable due to the fact that the permeability changes with the impacts, deformations, vibrations, etc., all the more so more than the initial permeability is high. Alloys of the type Mu-metal, Permalloy e.g. with an initial permeability from a few 100,000 will eventually be reduced to a few hundred. An object of this invention is to provide a cable with high To describe immunity in which the rigid magnetic Layer (s) by one or more flexible magnetic layers of the composite type, the effective permeability of which is of the order of 5 to 30, of which However, the value remains absolutely stable in the amount of permanent and temporary mechanical loads.

Of course, such layers 4 are also metallic because of their metallic nature Conductivity and / or their magnetic permeability have a thickness with a very weak skin effect, especially at high levels Have frequencies, whereas in practice they give rise to poor usability at the narrowest usable thicknesses because the electromagnetic fields cannot penetrate the metal. It is therefore another The aim of this invention is to describe a cable with high immunity, in which the magnetic metallic layer (s) through replaced one or more magnetic insulating layers or those with sufficient specific line resistance to reduce this skin effect, especially in the upper range of the frequencies in question.

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Of course, such layers 4 are also sensitive to highly magnetic ones, particularly in the case of high permeability Interference fields that saturate the magnetic materials. In particular, it may be close in the event of a lightning strike of the cable, or an electromagnetic pulse (EMP) due to a nuclear explosion, the effectiveness of the Layer, an effect which is of fundamental importance in the case of cables intended for use in military telecommunications systems Meaning is. Another object of the invention is therefore to describe a cable with high immunity, in which the magnetic is) Layer (s) due to their composite structure, i.e. with magnetic grains with high permeability in a non-magnetic plastic binder, is not very saturable, since the structure with multiple air gaps is not very saturable is.

It is also understood that such layers 4, depending on the length of the cable, can occur at a given frequency lead to line resonance phenomena, with current and voltage maximum and minimum values that differ because of the Imperfection of the cable carried over to the center conductor. Another object of this invention is therefore, in particular for high frequencies, the composite magnetic medium to be provided with an absorption in order to reduce or eliminate these resonance phenomena.

Finally, it goes without saying that such layers 4 are expensive to manufacture due to the price of the magnetic starting material (high permeability, thin Strips etc.) and its processing (special wrapping with no reduction in cross-section). The final aim of the invention is therefore to describe a cable with high immunity, in which the magnetic layer (s) is (are) by means of a

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conventional, fast and inexpensive extrusion process are made from cheap magnetic ferrite materials, and in particular the waste products thereof «

The composite magnetic material can be of the type as described in U.S. Patent Nos. 3,191,132 and 3,309,633 is; Correspondingly perfected material and its application are in particular in US patent application No. 855 dated November 25, 1977.

In the following description, the invention is referenced explained in more detail on various graphic representations to show their characteristics and the results achieved: in Figures 2, 3, 4, and 5 exemplified, the conventional asymmetrical coaxial structure is used taken into consideration; of course, the same considerations apply to all other symmetrical or asymmetrical ones Transmission structures, and especially the two linkages in the case of multi-conductor cables.

Fig. 2 shows schematically a cable according to the invention with high Immunity, with double armor and a magnetic flexible intermediate layer.

3 shows the transfer impedance as a function of the frequency with different cable types.

Fig. 4 shows schematically a coaxial cable with very high immunity according to the invention, with 3-fold armor and 2 magnetic intermediate layers.

Fig. 5 shows schematically an armored multi-conductor cable, with very high immunity according to the invention, particularly suitable for low frequencies.

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302550A -3-

One of the preferred embodiments of the invention is described in FIG.

In this figure, 1 is the center conductor of the coaxial cable,

2 the usual dielectric, 3 a high-quality conductive layer with regard to immunity to external interference fields. This layer can be in the form of a jacket or braid, with a low DC resistance: this value is defined in in fact the continuous transfer impedance and the one at very low Frequencies. With regard to scattering losses, it is optimally optimized, as described, for example, by EoHOMANN, NTZ No. 3, March 1968, pages 155-161 and EoF. VANCE IEEE; Transactions on EMC, May 19 75, pages 71-77, about a pronounced minimum of the transfer impedance Z at the middle frequencies to obtain.

In this figure, 7 denotes a magnetic layer according to the aforementioned patents: this layer of magnetic material in the form of a mixture of ferrite dust, iron carbonyl or other magnetic material that is bonded to a plastic or Elastomer is blended around the cable layers 1, 2 and

3 pressed using conventional cable manufacturing techniques; their thickness is between a few tenths of a millimeter to a few mm, depending according to the diameter of the coaxial cable 1, 2 and 3. Then form a conductive layer 8, consisting of a second braid (optimized according to the rules given), a coat of conductive paint, a band of metallized mylar and / or a pressed-on conductive mixed material the second armor. This type of color or mixed material is a person skilled in the art known and used by American companies

- Scientific Advances

- Emerson and Cuming

- Chomerics

- Custom materials

- Technical Wire Products, etc.

manufactured.

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The minimum thickness of this layer depends on its key parameters: the minimum frequency at which the Imitiunrtätsefekt is pronounced corresponds to a few skin thicknesses of the material the shift.

Fig. 3 shows the transfer impedance as a function of the frequency for different cables, expressed in relative terms Values in relation to the DC resistance of all armor connected in parallel.

In this figure, curve a) shows the transfer impedance of the Structure from Fig. 2, with a non-magnetic insulating means instead of the layer 7. The curve b) shows the transfer impedance the structure described; one sees an improvement of over 10 dB in the range from 10 kHz to almost 1 MHz. This improvement is such that up to approx. 200 kHz the structure according to FIG. 2 is even better than a cable with 3 braids, with not magnetic insulation between each armor.

It is easy to show that this improvement is proportional to the sum of the impedance of the outer surface of the armor 3, the Impedance of the inner layer of the armor 8 and the impedance of the loop formed from the space of the magnetic environment 7: this latter summand, together with the corresponding increase in the magnetic permeability of this milieu, brings improving immunity.

The structure according to FIG. 2 with a braiding of copper was subjected to Foucault current pulses of strong amplitude: to 200 A, the transfer impedance follows curve b), i.e. the cable retains its immunity, what with a magical layer of the Type mu-metal or permalloy would not o

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A second preferred embodiment according to the invention corresponds to a cable with very high immunity: it is described in FIG.

In this figure, 1 , 2 and 3 represent the actual coaxial structure as before. Two magnetic layers T and 7 ″ according to the aforementioned patents are separated from one another by a thin, conductive layer 8, which consists of a braiding applied according to the above rules, a jacket The outer armor 9 made of braiding, jacket, paint, metallized tape and / or conductive mixed material is covered with a protective insulating means 6.

A particularly interesting embodiment corresponds to this simultaneous extrusion of layers 7 ', 8 and 7 ", because of the low cost price and the high flexibility achieved and mechanical strength with the same transfer impedance as the best, expensive and sensitive structures with magnetic tape winding .

In these examples it has been assumed that the conductor to be protected is a coaxial cable: according to the invention, the part to be protected can also be double, triple, quadruple, etc. or finally made up of a number of different symmetrical or asymmetrical structures: ( armored or not, immunized or not), which are grouped under the same coat. In these examples too, the main consideration was immunity to the high frequency disturbances; at the low frequencies the immunity approaches the permanent resistance more and more, and ^; the inductive elements due to the permeability of the magnetic medium (s) naturally approach the value 0 with a frequency

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In the following example of FIG. 5, an embodiment of armor with high immunity according to the invention is shown given for a number of bundled cables, in particular for line frequencies. (In fact, currents of the same wave type, at 50, 60 or 400 Hz, represent currents with a strong amplitude a big problem for long distance transmission and signaling cables on board aircraft, ships, along electrically operated railway lines, etc.).

In this Fig. 5, the internal cables to be protected are labeled 10, 10, 10, 10, etc. They are surrounded by a first armor 3, a good flexible conductor (copper braiding, continuous sheath made of lead, etc.). Then, an insulating wound comes 7 ^e straiggepreßtem from magnetic material which is in turn wrapped with iron or steel strip material. 8

This is followed by a second layer of extruded material 7 ″, which in turn is wrapped with iron or steel strip material 9.

With such a complex structure, the multiple conductive and

includes non-conductive magnetic layers, the immuno-

effect at low frequencies is considerable and the anti-saturation effect optimal.

Usually the high permeability materials, i.e. those that are more easily saturated, are used inside, whereas those that are not very saturable (or made less saturable by means of effective air gaps due to a wrapping) with an air gap, and with a suitable winding step) materials are arranged towards the outside. Also normally should the most conductive material should be placed towards the inside of the structure, which also applies to long strides to the extent that in which the longitudinal resistance of a wrapping and a braiding with the cos function of the helix angle in relation

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to the axis varies. Of course, the various conductive armoring is connected accordingly to the points of the end connections.

Of course, the individual cables of such a complex structure can all or some of their part by means of the be protected according to the method according to the invention; in particular can simple armored cables have a flexible, outer, magnetic layer and with the global armor a protection represent according to the description.

Another object of the invention is os, the losses of the described magnetic mixtures at high frequencies, possibly increased by an additional controlled conductivity, to be used to suppress the resonance effects of the space or spaces between the armor.

Another object of the invention is to achieve the surface impedances described by adding with the maximization of the described impedance between the armor to a maximum to increase. For this purpose, in particular arrangements of the surface of the metallic conductors can be used by introducing them the normal skin effect (case of the combined cable according to FIG. 5 with magnetic tape strips), or the artificial one Skin effect as described in U.S. Patent No. 3,573,676.

Another object of the invention is to provide an external, absorbent end layer when extruding the structure of the complete cable add to increase the impedance of the outer surface and to provide additional protection against the common currents Wave type and against cross-coupling (in the case of adjacent Cable)"

Of course, the asymmetric ones in the examples apply coaxial structures described principles in the same way for any other symmetrical coaxial structure, for symmetrical

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and asymmetrical double, triple, quadruple, etc. structures under the same armor jacket, as well as for such
structures grouped together under the same armor jacket.

Furthermore, it goes without saying that the principles described also for a larger number of consecutive layers are applicable to achieve a very high immunity to interference fields.

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Claims (1)

Sponsors t_a η s p__r ü_c_h__e Flexible, armored, electrical cable for telecommunications and remote signaling entities, with high immunity to the interference fields, with at least two signal conductors and at least two flexible, conductive armor, which are separated from each other by at least one magnetic environment, characterized in that this magnetic medium consists of a magnetic mixed material which is flexible in its mass which is applied using conventional extrusion techniques. 2. Electrical cable according to claim 1, characterized in that that the inner, metallic, well-conductive armor is made of a flexible, non-conductive or only slightly conductive armor Layer of magnetic mixed material is covered, in turn by a second, outer, metallic, highly conductive Armor layer is covered. 3. Electrical cable according to one of claims 1 or 2, characterized in that the second highly conductive, metallic armor layer of a second non-conductive or slightly conductive layer of magnetic plastic that is flexible in its mass, as well as being covered by a third, outer, highly conductive armor layer. 4. Electrical cable according to one of claims 1 to 3, characterized in that the highly conductive metallic armor layers made of spun or braided tape, spun or Tape jackets and / or tapes made of metallized Mylar using continuous metallic conductors will. 130 0 13/0929 5. Electrical cable according to one of claims 1 to 3, characterized in that the second and / or possibly the third highly conductive armor layer made of a mixed material with metallic conductive particles in a flexible material. 6ο cable according to one of claims 1 to 5, characterized in that the layer (s) of magnetic mixed material by a
Interference of perite dust and / or other magnetic,
metallic dust of suitable grain size and concentration
are produced in a flexible carrier material to illustrate the effect of magnetic permeability, the losses due to absorption at a suitable high frequency »and one
high resistance to obtain a skin thickness greater than the thickness of the layer (s) in question, as well as an absorption of the high frequency resonance effect. 7. Cable according to one of claims 1 to 6, characterized in that the surface of the conductive metal and / or mixed material layers due to the utilization of the normal skin effect
(conductive magnetic alloys) or the artificial skin effect (metallic layers with variable permeability
and / or variable specific line resistance) has an increased surface impedance in the spaces surrounding the flexible magnetic environment. 8ο cable according to one of claims 4 or 7, characterized in that that one or more highly conductive metallic layers consist of magnetic strips, braids or sheaths with Optimized air gaps (pitch of the screw of the wrapping) in order to avoid local magnetic saturation. 13 0013/0929 9α cable according to one of claims 1 to 8, characterized in that that a magnetic mixed material outer layer is applied to increase the surface impedances and to introduce the losses by increasing the surface impedance and the resonances, against the disturbances of the common wave type and against the cross-coupling " 1 3 0 Q 1 3/0 9 2 9